The invention relates to a method for operating a parking brake module that is at least partially integrated into a compressed air generation system in the event of defects, including an electronic control unit, a plurality of solenoid valves for supplying a control pressure for actuation of the parking brake, and a relay valve receiving the control pressure for the ventilation and venting of at least one spring brake cylinder.
The invention further relates to a parking brake module, which is at least partially integrated into a compressed air generation system, including an electronic control unit, a plurality of solenoid valves for supplying a control pressure for actuation of the parking brake, and a relay valve receiving the control pressure for the ventilation and venting of at least one spring brake cylinder.
A compressed air supply system with connected consumers usually incorporated into a vehicle from a certain weight class onwards may be designed to deliver different supply pressures for the individual consumer circuits independent of one another. For example, a pneumatic service brake and an air suspension of the vehicle may currently be subjected to a maximum supply pressure of 12.5 bar, for example. Other consumer circuits, which usually derive no advantages of any kind from such a high supply pressure, may then be subjected to a lower supply pressure downstream of a pressure limiter. These consumer circuits can then be designed taking account of the lower supply pressure, thereby saving production costs, in particular. One example of a consumer circuit usually subjected to a lower supply pressure than the supply pressure of a service brake circuit is a parking brake circuit or a parking brake module of the vehicle, in which a supply pressure of between only 9 and 10 bar is provided.
In the event of an unwanted increase in pressure in the parking brake module, rising to the cut-out pressure of the compressed air generation system, due to a fault on the pressure limiter, for example, or if the high pressure gets into the low-pressure area via shaped seals, this leads to a persistent overloading of components of the parking brake module that are not designed for these high pressures, and of the spring brake cylinders activated via the parking brake module. The arrangement of a safety valve in the parking brake module, which solves this problem, is already known. The disadvantage to this, however, is that an additional valve takes up overall space and entails production costs, particularly if the parking brake module is at least partially integrated into the compressed air generation system.
The object of the present invention, therefore, is to obviate the need for a separate safety valve in the parking brake module, whilst maintaining the overpressure protection against excessive pressures in the parking brake module.
This, and other, objects are achieved in accordance with the present invention by a method for operating a parking brake module, in that a pressure in the parking brake module in excess of a normal pressure is detected, an ongoing compressed air delivery is interrupted, a reduced cut-out pressure of the compressed air generation system is set, and the pressure level in the parking brake module is reduced to the reduced cut-out pressure through repeated activation of the relay valve. These four steps in the method reliably serve to keep the pressure level in the parking brake module below a pre-definable threshold value, even if a defect triggers an unwanted pressure increase in the parking brake module and no separate safety is integrated in the parking brake module as overpressure protection. A pressure in the parking brake module in excess of a normal pressure can be detected directly or indirectly by one or more sensors, for example, it being possible to arrange individual sensors in the service brake circuit, on one of the spring brake cylinders, at the inlet or the outlet of the relay valve of the parking brake or in a trailer control module.
The method according to the invention is advantageously developed in that after interruption of the compressed air delivery and before setting a lower cut-out pressure, a regeneration phase is initiated until the original cut-in pressure is reached or until the original switching period has elapsed, so as to be able to discharge excess fluid more rapidly. Since a pressure increase in the parking brake module can occur only once the pressure level, at least in the compressed air generation system, has already reached a higher level than is admissible for the parking brake module, and a reduction of the pressure level in the parking brake module is sustainable only with a simultaneous reduction of the pressure level in the compressed air generation system, the fastest possible reduction of the pressure level in the compressed air generation system is advantageous.
It is especially preferred if, in the event of the pressure reduction through repeated activation of the relay valve, a cyclical pressure variation is induced in at least the one spring brake cylinder activated by the relay valve, the minimum pressure being not less than an opening pressure of the spring brake cylinder. The cyclical variation of the pressure level in at least the one spring brake cylinder activated via the relay valve serves for discharging fluid, that is to say, in particular, compressed air; from the parking brake module. Here the upper pressure level in the spring brake cylinder corresponds to the maximum pressure currently prevailing in the parking brake module, whilst the minimum pressure level is approximately 6 bar, care needing to be taken to select the minimum pressure level so that the activated spring brake cylinder will reliably remain open and the parking brake does not accidentally close.
It may be advisable, after reduction of the pressure level to the reduced cut-out pressure, for the originally higher cut-out pressure to be reinstated, if a consistently normal pressure level is detected in the parking brake module. If the fault that has occurred is reversible, that is to say there is no likelihood of a new, unwanted pressure rise in the parking brake module, or it is detected from measurements that a new rise in pressure consistently fails to materialize, it is possible following successful reduction of the pressure level in the parking brake module to again set the higher cut-out pressure of the compressed air generation system that was originally set as cut-out pressure, in order to maintain the energy efficiency of the compressed air generation system at a high level. An adjustable period covering multiple delivery and regeneration cycles, for example, may be deemed to be consistent.
Alternatively it is also feasible, after reduction of the pressure level to the reduced cut-out pressure, to continue to operate the compressed air generation system at the reduced cut-out pressure without any restriction of the functionality. In this way a reliable operation of all vehicle systems at a reduced pressure level can be ensured, without individual vehicle components, in particular the parking brake module, being damaged due to an unwanted, high pressure load. The vehicle can thereby be moved in road traffic until an opportunity for repair presents itself.
The parking brake module of generic type is developed in that the electronic control unit is suited to detecting an unwanted, high pressure in the parking brake module, interrupting any ongoing compressed air delivery, setting a reduced cut-out pressure of the compressed air generation system and reducing the pressure level in the parking brake module to the reduced cut-out pressure through repeated activation of the relay valve. In this way the advantages and peculiarities of the generic method are implemented in the context of a device.
This device is advantageously developed in that the electronic control unit is suited, after interruption of the compressed air delivery and before setting a lower cut-out pressure, to initiating a regeneration phase until the original cut-in pressure is reached or until the original switching period has elapsed, so as to be able to discharge excess fluid more rapidly.
It is especially preferred here if the electronic control unit, in the event of a pressure reduction through repeated activation of the relay valve, induces a cyclical pressure variation in at least the one spring brake cylinder activated by the relay valve, the minimum pressure being not less than an opening pressure of the spring brake cylinder.
The electronic control unit may appropriately be suited, after reduction of the pressure level to the reduced cut-out pressure, to reinstating the originally higher cut-out pressure.
Alternatively the electronic control unit may also feasibly be suited, after reduction of the pressure level to the reduced cut-out pressure, to continued operation of the compressed air generation system at the reduced cut-out pressure without any restriction of the functionality.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawing.